Deformation in the Long Valley Caldera, California, 1983–1984

Measurements of deformation in and around the Long Valley caldera in the interval July 1983 to August 1984 indicate that deformation is proceeding at a roughly uniform rate and that the net deformation for the year is about the same as for the preceding year. The 1983–1984 deformation of the 40‐line trilateration network can be approximated as the effect of the expansion (0.022 km3) of a spherical magma chamber located 10 km beneath the resurgent dome plus right‐lateral slip (50 mm) on the uppermost 2 km of the 8.5‐km‐long 1983 rupture surface in the south moat of the caldera. This same model furnishes an approximate fit to the tilting observed at six 1‐km aperture bench mark arrays within the caldera, although the quantitative fit lies somewhat outside the estimated observational error. The model, though obviously too simple to furnish a detailed fit to the complex process of magma chamber reinflation, does furnish a reasonable overall picture of the deformation.